Glass fibers have been commonly incorporated in thermoplastic molded objects and other cured plastics for added strength and durability. The glass fiber is introduced in a mold where resinous plastic is then injected such that the glass fibers become imbedded into the final formed article. It has been found advantageous to form a self supporting preform out of glass fibers and position the preform into the mold before the resinous plastic is injected. One article which has been found to be advantageously made in this fashion is a motor vehicle bumper.
An expeditious process for forming the preform has been found to be a directed fiber spray process. The process includes blowing chopped glass fibers onto a preform screen. Immediately following the fiber placement, a binder agent is sprayed on and allowed to cure which sets the chopped fibers in place.
Conventional preforms for reinforced motor vehicle bumpers have glass fibers deposited throughout the part in a uniform manner. The preforms are made by thermoforming rolled goods such as Fabmat (tm) or by the described directed fiber spray process.
The preform is then inserted in a mold and resinous plastic is then injected into the mold to bond with the preform to form a structural reinforced injected molded article commonly referred to as a SRIM. Often the SRIM is trimmed to form scrap which is currently shipped to a land fill.
The known processes do not use layers of glass in the most efficient manner. The uniform distribution of woven roving or chopped glass fiber leads to inherent inefficiencies. Areas of lowest stress in a SRIM article have the same density and same type of costly glass fiber as the highest stress areas. Furthermore, many SRIM articles are trimmed of excess flange material. Additionally, cut outs are often cut from the SRIM article. Traditionally, all the trimmed flange material and cut out material has been considered waste product.
Recycling waste trim is becoming more economically feasible and environmentally compelling due to the increasing value of the waste material, the increasing costs of solid waste shipping and disposal, and the decreasing availability of landfills. One potential use for recycled SRIM material is in successive SRIM articles. The recycled SRIM material can be used as an expense saving substitute for expensive glass fibers. However, the need for recycling waste trim must be balanced by the need to maintain the structural integrity of structural reinforced injected molded plastic parts.
What is needed is a preform that has higher density levels of glass and glass fiber in higher stress regions of the final object and recycled scrap SRIM in areas of relatively lower stress such that the integrity of the final molded part is not jeopardized. What is also needed is a process for manufacturing such a preform. In this fashion, a SRIM article is expeditiously manufactured using recycled SRIM material without sacrifice in its structural integrity.